Pressure vessel



Feb. l5, 1944. I H, J, K RR Re. 22,436

PRESSURE VES SEL Original Filed May 25, 1957 i INVENTOR. Howard J Kerb Reissued Feb. 15, 1944 raassuas VESSEL I HowardJ. Kerr, Westfleld, N. Jsassignor to The Babcock a Wilcox Company, Newark, corporation of New Jersey Orig nal No.

Serial No. 144,755,

for reissue Ncvemb 1s. 1., in

2,183,043, dated. December 12, 1939,

May 25, 1937. Application cr 29, 1941, Serial No.

.- 6 Claims. (01. 148-4) This invention is a pressure vessel and method of forming the same with tubular welded connections irrespective of a wide difference in thickness dimension of the wall of the tube with respect to that or the wall of the vessel to which the tube is Joined. j

The dimculties attendant upon joining metals of different thickness by fusion welding are too well known to need detail statement herein. The problem solved by the present invention is for steam generators and wherein the superheated steam is received into the header I through tubes 2. r

In order to provide the juncture between the header I and a tube 2 the header wall is drilled clear through as shown at 3 in Fig. 2 for the inside diameter of the tube, the drilling isthen counterbored as at 4 from the outside to a selectthat of joining a thin wall'tube to a thicker wall pressure. vessel with a depth of fusion welded juncture adequate for the strength of the union but without danger of impairing the strength of the tube wall should any non-uniformity exist in the region of the weld juncture between tube and vessel wall.

A further feature of the invention resides in so forming the union between the tube and vessel wall that the tube wall sustains the internal pressure without imposing any appreciable pressure load upon the weld.

Additionally the invention provides for satisfactorily accomplishing afield welded joint between a tube and vessel of dissimilar metals where the metals are such that it would be difiicult, unsatisfactory and expensive to perform the joining of such metals in the field.

A still further advantage of the present invention is that where the tubes and vessel structure are used with high temperature fluids..such as superheated steam, for instance, conveyed to the vessel by the tubes, the conductivity of the juncture is such that sudden changes in temperature, which might otherwise tend to impair the permanency of the joint, is minimized.

.With the foregoing and other objects in mind I will now describe practical embodiments of my invention which I have illustrated in the accompanying drawing forming a part of this specification and wherein- Fig. l is a transverse section through a pressure vessel having a number of tubes joined therewith.

Fig. 2 is a similar sectional view showing the tube seat prior to welding.

Fig. 3 is a transverse section of a shop-assembled tubeend ready to be welded, in the field, to the pressure vessel. 7

Fig. 4 is a transverse sectional .view of the tube of Fig. 3 welded into the vessel, and

Fig. 5 is a transverse sectional view of the tube welded to the vessel where the tube-receiving portion is built up of weld deposited metal.

In the invention as shown in Fig.1, the disrlosure takes the form of a superheater header ed diameter and depth for receiving the end of an enveloping sleeve 5 welded to the tube 2 finished flush with the end as shown at l and which is further fillet welded to the tube 2 at the other end, as indicated at 8. The assembled. tube 2' and sleeve 5 are then entered into the counterbore I to its full depth and fillet welded circumferentially as at 9.

This method of construction has several advantages, for instance, the end of tube 2 and its encompassing sleeve 5 are prepared in th shop where welding conditions are conducive to greater uniformity of product than is the case in field welding, and the danger of poor deposit or burning through the thin wall of the tube 2 are at a minimum; the finishing of the joint in the field by uniting the tube to the drum, where conditions are less uniform than in the shop, then embraces asingle weld deposit 9 clrcumferentially of the sleeve 5 where the added thickness of metal due to. the sleeve 5 and the poor thermal bond between the unwelded length of tube and sleeve produce a condition which is commensurate with welding together two pieces of greater thickness than would be the case if the tube itself were welded directly to the vessel body, and consequently greater welding heat may be used with better penetration and less danger of burning through the thinner stock.

Also for high temperature and high pressure conditions alloys are employed which, for instance, for the vessel and the tube may render it impossible or impracticable to directly unite the vessel and tube, whereas in the present construction and method the intermediate sleeve 5 may be of a metal having characteristics which render it suitable for welding both to the tube and to the vessel even though each be of different character and unsuited to each other so far as joining by fusion welding is concerned; and here again it is obvious what convenience this furnishes where, as in a steam'generator, the vessel and the tube may each be formed in the shop and regardless of the suitability of the metals of the tube and vessel metals, may be satisfactorily joined in the field by fusion welding.

Thermal shock due to superheated steam entreated as mentioned above.

terms the-vessel. through the tube is minimized by reason of the poor thermal juncture between the tube and sleeve and the sleeve and vessel, except at the locations where they are united by the weld deposit, and hence the joint is subjected to a less rapid flow of heat and greater uniformity with consequentlyless strain upon the joint at times of change in temperature.

In the modification shown in Figs. 3 and 4 which carries the same reference characters as ,g Figs. 1 and 2 for similar parts, the tube 2 is of appreciably thinnenwail than the surrounding sleeve 5 and consequently even more likely to be burned through in welding than is the case with the tube 2 of the form shown in Figs. 1 and 2, and hence there is thus an even greater 'advantage.

Further, it is to be noted that at the location where the weld makes the joint with the thick metal oi the vessel it is not the tube I alone which carries the pressure of the fluid within the vessel and tube, but the tube 2 plus the sleeve I so that in this area, where deep fusion is required, with possibility of burning, the strength of the tube wall remains unimpaired.

In the form of the invention shown in Fig. 5, the body of the vessel i has weld deposited thereon the additional thickness ll subsequently ma-. chined flat on its'face I l and bored and counterbored similarly to the bore and counterbore of Fig. 2. but such that thesleeve I and tube 2 are seated within the added metal. 'The added metal may be of an alloy different from that of. either vessel I, sleeve I and tube 2 but readily united by fusion welding to sleeve I in the same manner as previously described. i

The advantage oi this construction is that, for instance. in the welding of 4-6 chrome steel it is necessary to preheat the steel before welding, keep the piece from cooling down after welding lmtil placed in a furnace where it is heated up to approximately 1600 F. and furnace cooled, then heated up to 1350' F. and furnace cooled to black, so that obviously in making such a construction if it were attempted to weld 4-6 chrome tubes to a header of 4-6 chrome steel it would be an almost impossible job to accomplish this except under shop conditions; and even then it would be diiiicult.

In the present instance the design is so arranged that the sleeve on the ends of the 4-6 chrome tubes 2 is of carbon molybdenum steel, and which assembly, after welding, is heat header then under shop conditions a suillcient thickness of carbon molybdenum steel the proper heat treating may again be performed in the shop. The thickness of carbon molybdenum steel provided on the header is such that when the carbon molybdenum sleeve 5 is subsequently.

1 m eombinaticn, a thick walled pressure ves- In welding to the aasse sel such as a drum or header having a wall portion providing a tube seat; a tube adapted to be a fitted to the vessel at the tube seat, at least one of said elements being formed of metal having such characteristics that it is locally so hardened by'air cooling after welding thereto that subsequent heat treatment is necessary if restoration of its original characteristics is to be approached; and a body of metal of diflerent chemical constituency and having dissimilar hardening characteristics welded to the element having said characteristics and adjacent the tube seat zone before the fitting of said elements together, said body of metal providing means for connecting the elements together by a separate weld eil'ected after the fitting of said tube to the tube seat.

2. In combination, a thick walled pressure vessel such as a drum or header having a wall portube to the tubeseat of the vessel. said body of tion providing a tube seat, said vessel being formed of a metal having such characteristics that it is not locally so hardened by welding metal thereto that subsequent heat treatment is necessary if restoration of its original character istics is to be approached; a tube adapted to be fitted to the vessel at the tube seat, said tube being formed of a metal having such characteristics that it is locally so hardened by welding metal thereto that subsequent heat treatment is necessary if restoration of its original characteristics to be approached; and a body of metal of different chemical constituency than that of said tube and having dissimilar hardening characteristics welded to said tube adjacent, the tube seat zone thereof and before the fitting of said thereto that subsequent heat treatment is necessary if restoration of its original characteristics is to be approached: a tube adapted to be ,fitted to the vessel at" the tube seat, said tube being formed of a metal having such characteristics that it is not locally so hardened by welding metal thereto that subsequent heat treatment is necessary if restoration of its original characteristics is to be approached: and a body of metal of diflerent chemical constituency than that of said vessel and having dissimilar hardening characteristics welded to said vessel adjacent the tube seat-zone thereof and before the fitting of said tube to the tube seat of the vessel, said body of metal providing means for connecting the tube to the vessel by a separate weld eiiected after the fitting of said tube to the tube seat of the vessel.

4. The method of welding together two pieces of metal, at least one of which is subject to change in its physical properties adjacent the weld by the welding operation, which comprises welding an extension of metal which is not subiect to such change to the edge oi said piece subject to change to protect the latter from undergoing changes in physicaiproperties as a result of subsequent welding ope rations. heat treating the composite piece to provide the desired physical properties in the metal thereof, and subsequently welding laid pieces together with said added metal between the weld and the original piece subject to change.

5. The method of welding together two pieces of metal, at least the first at which is subject to change in its physical properties adjacent the weld metal being such that the heat conducted so raise the temperature of the first piece that heat treatment is required.

6. The method of welding to a pressure vessel a tube which is subject to such change in its physical properties adjacent the weld by the welding operation that heat treatment is required, which comprises welding an extension of metal which is not subject to such change to the tube to protect the letter from undergoing changes in physical properties as a. result otsubsequent welding operations, heat treating the composite tube and extension to provide the desired physical properties in the metal thereof, and subsequently welding said pressure vessel and tube together with said extension between the weld and the original piece subject to change.

- HOWARD J. KERR. 

